nextTicketNumber() was using count()+1 which collides when tickets
have been deleted. Now queries MAX number via SUBSTRING ordering so
the generated ticket number is always unique.
- Bootstrap (critical): settings/create/index no longer 403 on fresh install.
Site admins (admin/super_admin) can access settings when 0 groups exist.
First group creation seeds default priorities (Low/Medium/High/Urgent).
Index shows friendly first-run splash. Create shows warning + settings link.
- Internal notes leak (high): submitters can no longer receive is_internal
messages via ticket show, index detail panel, or any Inertia prop.
filterMessagesForRole() strips internal notes for non-agents.
- Arbitrary assignee (med/high): update() now validates assigned_to against
actual agent-access users for the ticket's group server-side.
- Cross-group priority/project forgery (medium): store() and update() now
verify priority_id and project_id belong to the ticket's own group (or
are global for priorities).
- Foreign message_id on attachment upload (medium): message_id is now
validated to belong to the current ticket, not just any message row.
